Cryogenic materials, such as liquid helium and/or liquid nitrogen, are materials that are gases under normal atmospheric conditions, but that become liquid when pressurized and sufficiently cooled. Transfer systems for cryogenic materials typically include pipes joined together using welded flanges and/or detachable couplers. The pipes are often vacuum jacketed to minimize the amount of heat entering into the system and reaching the transferred material. When detachable couplers are utilized, the coupled joint represents a discontinuity in the vacuum jacket around the pipes, because of the inherent detachability of the coupler. Thus, where a detachable connection between two pipes designed to carry cryogenic material is desired, couplers such as “bayonet” couplers are often utilized to minimize the amount of heat conduction at the joint.
Conventional bayonet couplers are appropriate in systems designed to transport materials maintained in a pressure range of a nominal 150 pounds per square inch (“PSI”) to a maximum of 300 PSI. To address heat leakage, conventional bayonet couplers provide an overlapping joint that operates to insulate against heat conduction. The overlapping joint is formed by an elongated annular extension formed on a male hub that is insertable into an aperture of a female hub, such that heat conducted from the atmosphere must travel through the hubs and along the overlap before it is conducted to the flow path. In this regard, the performance of conventional bayonet couplers, in terms of addressing heat conduction, is primarily a function of the thickness and length of the overlapping joint between the male and female hubs, as the structure of the overlap is what conducts the undesirable heat, e.g., the heat enters the hub from the atmosphere and traverses through the hubs and along the overlapping joint where it reaches the connected pipes.
Unfortunately, however, detachable joints, and specifically, the primary means for providing detachable joints in cryogenic systems, e.g., conventional bayonet couplers, are impractical where pressures are above 300 PSI. In such systems, the thickness of the overlapping joint, e.g., the thickness of the male extension and mating female receiver, must be significantly increased to accommodate the additional pressure. Increasing the thickness, however, means that the length of the male extension and female receiver must also be increased several times to accommodate the increased heat conduction provided by the increased thickness. In this regard, conventional bayonet couplers for systems where the pressure is above 300 PSI would have to be so large, e.g., on the order of several feet, that manufacturing becomes impractical both from a cost standpoint and feasibility standpoint. In other words, hollowing out a several foot long piece of raw alloy material stock to form the overlapping portion of a bayonet coupler is not cost effective or practical. Rather in high pressure systems a welded connection with an overlapping vacuum jacket is utilized, albeit without an efficient means for detaching, e.g., cutting of the weld.
Another problem with conventional bayonet couplers utilized in cryogenic systems is leakage of material. Such leakage often occurs during startup and shut down where low temperature material flow contacts the joints formed by the coupler causing expansion and/or contraction of the same that results in leakage.
It is also known in the art of cryogenic fluid storage systems to use vapor shielding as an insulator to prevent heat transfer to a stored or transported fluid. Typically, in such systems, boil off of the cryogenic fluid from the storage system is routed through tubing, e.g., coils or wraps of tubing, to another storage container. The coils or wraps of tubing intercept heat at junctions in contact with the outside atmosphere and reduce the heat transfer from the environment to the stored cryogenic fluid.